Method and a device for protective encapsulation of pipe loops installable on the seabed

ABSTRACT

A method and a device for the protective encapsulation of an oil or natural gas pipe loop within an outer jacket or cover for installation on the seabed, where the end portions of the pipe loop are coupled to an underwater structure. The protecting encapsulation of the pipe loop within the cover or outer jacket is performed on the surface and the pipe loop is lowered, substantially completely protected, to an installation position. On the seabed, the outer jacket or cover in which the pipe loop is confined may be covered with a layer of chippings.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for protective encapsulationof pipe loops installable on the seabed or one or more parts of pipes orpipelines, respectively, in the need of local protection againstexternal loads, such as falling loads, trawl appliances drawn laterallyacross the pipe loop or the pipeline, as well as to counteract that sandand gravel mass beneath the pipe is being washed out, said pipe loop orother pipe being intended to convey oil and/or gas which can give riseto partly large temperature variations, and following expansion andcontraction phenomena, and wherein the pipe loop or other pipe duringthe installation is lowered down from surface position, and wherein thepipe loop or other pipe in operative position of use on the seabed issurrounded by a protective cover which, preferably, in a finaloperation, is covered by a layer of chippings, or is kept in position inanother, not specified way, e.g. by means of anchors.

Likewise, the invention relates to a device for protective encapsulationof a pipe loop or other pipe for the same general purpose, comprising aprotective cover, possibly consisting of a number of joinable sections,jointly corresponding to the length of the pipe loop and shaped anddesigned in order to accommodate and surround a correspondingly longpipe portion.

Said protective cover or cover section, respectively, may have a closed,locally perforated, e.g. triangular cross-section with rounded cornersand a flat floor-space/bottom wall to be placed against the seabedsurface and which, internally, does not counteract the extensions andcontractions of the pipe due to temperature alternations.Seabed-installed pipes and pipelines conveying gas and/or oil may varyto such a degree that the pipe will have to lengthen/shorten itself e.g.two metres at each end. A temperature of up to 110° C. is an adequateexample associated with oil and/or gas temperature when conveyed inpipes along the seabed.

2. Background

Pipe loops of this kind extend usually between underwater structures,but the protection method and device, respectively, according to theinvention may as advantageously be used for pipe or local pipe sectionsof similar kind.

In such cases, in accordance with prior art technique, a pipe loop isfirst lowered down by means of a so called yoke, a kind of elongate boominsignificantly exceeding the shortest distance between the outer endsof the pipe loop, the pipe loop being attached to the boom, fixing meansbeing fastened to the boom for the lowering operation. After the pipeloop's lowering and positioning on the seabed, a protective cover ismounted around the pipe by means of divers and/or underwater vessels.Thereafter, a further vessel will provide covering of the pipe loopincluded within the protective cover, with chippings.

Known and conventional technique is very time-consuming and expensive.

BRIEF SUMMARY OF THE INVENTION

The object of the invention has been, with simple and cheap means, toindicate a method and provide a device for protective encapsulation of apipe loop or other pipe installable on the seabed, wherein theinstallation of the pipe, from the installation starts until the piperests on the seabed in protected condition, can be carried out in aconsiderable shorter time and with fewer vessels than before.

The object is achieved by proceeding in accordance with thecharacterizing clause of the first method claim. The first apparatusclaim defines a suitable device for carrying out this method.

According to the invention, the protective cover is mounted on the pipeloop or other pipe in surface position, for, thereupon, to be lowereddown to the installation place on the seabed from a surface vessel in atleast partly protected condition.

This step involves that one can not only perform encapsulation of thepipe loop within the protective cover/jacket above water (on the placeof production) instead of on the seabed and, thus, perform the necessaryworking operation on a far more convenient place where, moreover, theworking conditions may be arranged optimally for the particularoperations; besides this, the significant advantage is achieved that therequired fasteners for the lowering-down wires from the surface vesselnow may be provided on or attached to, respectively, the protectivecover/jacket or the joined sections thereof, respectively. This resultsin that lowering of a pipe loop does not require the previously usual,very elongate yoke, and one is spared from releasing the pipe loop fromthe yoke at seabed level.

When the pipe loop thusly encapsulated within the protective cover hascome into position on the seabed and each of its two ends has beencoupled to a underwater structure belonging thereto, one can, if desiredor necessary, place a layer of chippings on top of the protective coverwith the pipe loop encapsulated therein. For example this can bedesirable in fairway where bottom trawl fishing is usual. The layer ofchippings will usually acquire the shape of an approximately triangularcross-section with a rounded top, and a bottom trawl will readily crosssuch a hindrance without getting entangled therein and without damagingor displacing the cover with the therein positioned, freelyexpanding/contracting pipe loop.

The protective cover surrounds the pipe with a clearance, and thisclearance may, at least partly, advantageously be utilised for thefilling of insulation material. Oil which becomes stationary within thepipe during a brief stoppage, will, thus, be insulated against coolingand solidification, so that these undesired states are delayed. Furtherheating may take place by installing heating pipes directly on the pipeloop.

In the cover or in one or more cover sections, respectively, in thebottom wall, through-going holes may be formed in order to, during theinstallation of cover/jacket with encapsulated pipe, be capable ofletting seawater into the space between the outside of the pipe and saidinsulation's inside.

Hoisting means in the form of fasteners on cover and, possibly, on pipeloop may consist of attachment armatures in steel and/or soft hoistingstraps for wire. Fasteners on the pipe loop are, preferably, releasable,so that they can be removed when the pipe loop included within theprotective cover has arrived into position on the seabed and the endsthereof each has been coupled to an underwater structure belongingthereto. Prior to such a coupling operation, cover and pipe loop arereleasably attached to each other, so that pipe loop and cover becomemounted in correct positions in relation to each other. Subsequently tothe pipe loop's interconnection between the structures, the connectionbetween cover and pipe loop is released.

BRIEF DESCRIPTION OF THE DRAWINGS

The method and the device according to the invention is furtherexplained in the following, reference being made to accompanyingdrawings, in which:

FIG. 1 in a top plan view illustrates the typical course of a pipe loopencapsulated within an external jacket consisting of a plurality ofjoined cover sections, and wherein the ends thereof each is intended tobe coupled to an underwater structure (not shown) belonging thereto, ina manner known per se;

FIG. 2 is a cross-sectional view along the line II—II in FIG. 1 throughthe uppermost seabed layer, the cover according to a first embodiment,as well as the pipe;

FIG. 3 shows a cross-section corresponding to FIG. 2, wherein the coveris of second embodiment, a layer of chippings being placed on top of theexternal jacket.

DETAILED DESCRIPTION OF THE DRAWINGS

First, reference is made to the general view of FIG. 1 where a dottedpipe loop 10 which may have an arbitrary course, here is shown tocomprise two angled end portions 10 a and a long, straight, intermediateportion 10 b.

The pipe loop 10 is, in a surface position, encapsulated within anexternal cover/jacket 12 consisting of a number of straight and curvedsections 12 a joined together in a way not specifically indicated, e.g.by means of annular, outwardly directed flanges, wherein adjacentflanges have aligned bolt holes for interconnecting bolts or equalattachment means.

The advantage of encapsulating such a pipe loop or another pipe or pipeportion to be mounted on the seabed and, possibly, coupled to underwaterstructures (not shown), is not only the possibility of working undersignificantly more controllable conditions which readily may be arrangedfor suitable implementation; it is also advantageous that theencapsulated pipe no longer will need the previously described bracingyoke carrying attachment armatures for the fastening of hoisting wirefor the pipe loop's lowering from the surface down to the seabed, and towhich the pipe loop must be fixed prior to said lowering operation andreleased from subsequently to its landing on the seabed. Hoisting of theyoke represents a further working operation which now is facilitated.

With a pipe loop encapsulated within said cover or jacket, the latterwill stabilise the pipe loop during the lowering thereof and will carryattachment armatures for hoisting wires. Alternatively, at certainintervals along the longitudinal extent of the pipe loop, the loop maybe equipped with fasteners, e.g. in the form of lifting straps placedaround the pipe. For the description of details of the pipeloop-encapsulating outer protective cover/jacket 12, reference is nowmade to FIG. 2, showing a cross-section (II—lI in FIG. 1) of a firstembodiment of a cover.

Here, seabed level is denoted at reference numeral 14.

In this embodiment, the cover/jacket 12 (more exactly its individual,joinable sections 12 a) is formed in two parts 12′, 12″ divided along alongitudinal plane of division. The top part 12′ has an angled (inverseV-shaped) cross-section having an obtuse top angle, and both top andbottom part are outermost terminated by angled, perforated flangeportions 16 which, therebetween, accommodate slopingly downwardlydirected plates 18, through-going bolts 20 locking flange portions 16 toeach other, simultaneously as they clamp the inclined plates 18 firmlybetween the flange portions 16. The inclined plates 18 are intended tocounteract excavation of mass beneath the cover 12. Length and shapethereof may vary in accordance with bottom conditions and need.

In the bottom part 12″, holes 22 are provided in order to let inseawater during the installation of the cover/jacket and the therewithinencapsulated pipe loop 10, the top part 12′ being formed with a centralaperture 24, which serves partly to let out air as it is displaced fromthe cavity by seawater through the hole 22, partly as passage for alifting strap 26, which is placed directly around the pipe 10. On thetop part 12′ of the cover, external attachment armatures may be mountedin the upper portion thereof, for the fastening of one or more hoistingand lowering wires (not shown). Of course, also the lifting strap 26will be attached to such a wire.

Internally, within the cover/jacket 12, insulation material 28 has beenplaced, with the purpose of thermically insulating the fluid, e.g. oil,being conveved through the pipe loop, so that the oil temperature is notreduced so rapidly during a brief stoppage that the oil solidifies.

On the underside of the bottom part 12″ of the cover/jacket 12,plate-shaped weight elements 30 may be attached, constituting sinkerand/or stabilisation.

The embodiment in FIG. 3 is very much like the one shown in FIG. 2, andmutually identical parts and portions are allotted the same referencenumerals. Only parts differing from those of the embodiment according toFIG. 2 will be described in addition to immediately adjacent portions.

In the embodiment shown in FIG. 3, the pipe loop 10 is not assigned anylifting straps. Instead, the top part 12′ of the cover/jacket 12 isequipped with an upper, centrally placed hoisting means 32 displaceableup and down in a central aperture 24 in the top part 12′. The hoistingmeans has an upper fastener in the form of an eye or a ring and a lowerstop, the upper curvature thereof being complementary to the internal,downwardly facing curvature of the top part 12′ in the area around thecentral aperture 24. When lowering wires (not shown) in surface positionare attached to the fasteners of the hoisting means 32, these are firstdrawn upwardly until their lower stops come to rest against theunderside in the area for the central aperture 24 of the top part 12′,whereupon the lowering of cover 12 with pipe loop 10 encapsulatedtherein may be carried out by means of the wires. Also, fixed liftingears in the cover may be used.

When cover/jacket 12 with pipe loop positioned therein, but withprojecting outer end portions each intended to be coupled to anunderwater structure, is installed on the seabed 14, it will beadvantageous to cover the cover/jacket 12 with a layer of chippings 34or similar stone material.

Between the insulation layer 28 in the cover/jacket and the pipe's 10external shell face, a redundant clearance suitably exists. The inner,upwardly facing surface of the bottom part's 12″ insulation layer 28has, preferably, a plane course, so that it does not counteract thepossible longitudinal expansion/contraction movements of the pipe loop.

What is claimed is:
 1. A method for protective encapsulation of pipeloops (10) or one or more parts of pipe or pipelines, respectively,installable on the seabed (14) and of the kind needing local protectionagainst external loads, such as falling loads, bottom trawl equipments,etc., and for, possibly, counteracting washing out of mass from beneaththe pipe (10), particularly pipe loops (10), etc., serving to convey oiland/or gas which may introduce large temperature variations into thesystem, accompanied by expansion/contraction phenomena, the methodcomprising: encapsulating the pipe loop (10) within a protectivejacket/cover joined together of joined longitudinal sections (12 a)wherein the pipe loop (10) or similar pipe/pipeline is encapsulatedwithin the jacket/cover (12) in a surface position, the jacket/cover(10) being equipped with fasteners (32) for a hoisting and/or loweringwire; and lowering the encapsulated pipe loop (10) to the seabed (14),where the outer ends of the pipe loop (10) are coupled to any underwaterstructures, whereupon the cover/jacket (12) with the pipe loop (10)confined therein, is covered with chippings (34).
 2. A device forprotective encapsulation of a pipe loop, comprising a jacket/cover (12)consisting of joined/joinable, longitudinal sections (12 a) shaped tosurround a pipe loop (10) or similar pipe/pipeline with a clearancetherebetween,. characterized in that the jacket/cover (12) or each ofthe longitudinal sections (12 a) thereof, respectively, is divided intoat least two parts, a top part (12′) and a bottom part (12″) which arejoinable, through flange portions (16) and bolt connections (20) whereinthe bottom part (12″) substantially exhibits a supporting face for thepipe loop (10), the top part (12′) having an arched or polygonalcross-section, convexly curved in an upward direction.
 3. The device asset forth in claim 2, characterized in that the cover/jacket (12) oreach of the sections (12 a) thereof, respectively, is provided with aninternal insulation layer (28).
 4. The device as set forth in claim 2,characterized in that the cover/jacket or each of the sections thereof,laterally is provided with at least one laterally slopingly downwardlydirected plate-like element mounted to the respective jacket/coversection through the co-operating flange portions (16) and boltconnections (20) of the top part (12′) and the bottom part (12″).
 5. Adevice for the protective encapsulation of a pipe loop, comprising: acover/jacket (12), having an inner, side consisting of joined/joinablelongitudinal sections (12 a) shaped to surround a pipe loop (10) orsimilar pipe/pipeline with a clearance therebetween, wherein thecover/jacket (12) or each of the longitudinal sections (12 a) thereof,respectively, is divided into at least two parts, a top part (12′) and abottom part (12″) which are joinable, through flange portions (16) andbolt connections (20) wherein the bottom part (12″) substantiallyexhibits a supporting face for the pipe loop (10), and the top part(12′) having an arched or polygonal cross-section, curved in an upwarddirection; and at least one hole (22) in the bottom part (12″) of atleast one cover/jacket section (12 a), in order to let seawater into thespace between the pipe loop (10) and the inner side of the cover/jacket(12) during the installation, and that the top part (12′) is formed witha central aperture (24), through which air displaced by water flowingin, can escape.
 6. The device as set forth in claim 5, wherein ahoisting strap (26) placed around the circumference of the pipe loop canpass through the central aperture and serve as a fastener for a loweringwire for lowering the cover/jacket (12) with the pipe loop confinedtherein from surface position to seabed (14).
 7. The device as set forthin claim 5, having a hoisting means (32) with a fastener for a loweringwire wherein the hoisting means is displaceable supported in the centralaperture (24).